Modern computer systems typically have a wide variety of internal electronic devices that communicate across an internal bus system. Among other things, those electronic devices may include memory chips, microprocessors, graphics processors, and power supplies. Many of those electronic devices are mounted to standardized circuit boards (known as “cards”) that are removably coupled to the bus system. For example, a microprocessor and accompanying components may be mounted to a peripheral component interconnect card (“PCI card”), which itself is secured to a card slot on a PCI bus.
PCI cards typically are easy to remove from their slots and, in a like manner, may be easily slid into their slots. Accordingly, a person may replace an existing PCI card having an older, less efficient electronic device (e.g., an older microprocessor) by first removing it from the slot, and then inserting into the slot a different PCI card having a newer, more efficient electronic device.
Some computer systems must be completely powered down to replace a card. If not powered down, unanticipated currents and voltages may damage internal electronic components, or harm the person replacing the card. Other computer systems, however, are not powered down to replace cards. Instead, some other systems simply power down only the slot or bus having the card being replaced. Such systems are known in the art as “hot plug” systems. After the card is placed in the slot, the computer should recognize it and operate accordingly. If not, then logic may be added or modified to ensure that the computer system successfully operates the components on the newly added card.
When powering down, some hot plug systems maintain an electrical connection between the bus and corresponding bus controller (also known as a “bus driver,” which controls bus operation). Moreover, some such systems cause that connection to have a very low impedance and a ground potential. Undesirably, other electronic devices within such systems may generate spurious signals when they detect a low potential (i.e., ground). In other words, low active devices may produce unintended signals if they detect the low impedance ground. Those undesired signals could disrupt or damage the system.